$4.$ The profit calculation in the readings and class assumes you borrow at a fixed interest rate to finance investments. An alternative way to borrow is to short$-$sell stock.

a$.(10$ pts$.)$ What complications arise in calculating profit if you finance a $$1,000$ investment by shorting a stock, rather than borrowing $$1,000$ at a fixed rate?

b$.(15$ pts$.)$ Support your answer above by using at least one timeline to illustrate your reasoning.